I admit it. I am a troll. I troll, sometimes comment, on a couple of triathlon forums. Next to what tires should I get to race on, and what is the best multisport car, swimming is a favorite topic of discussion. It's seldom that I get drawn into the discussions. If I have something that I think might be of help, I'll post it.
One of the things that we talked about at our early season swim clinic and recent small-group IMTX camp was knowing your paces. And pace stretches to basically include 'data'. Watts. Swim paces in the pool. Run paces with and without a GPS. When I say that I mean that you can develop an internal GPS for almost everything. Watts and perceived exertion. Run pace and perceived exertion.
The swim is a bit more difficult, but it helps to know what your swim paces 'should' be in the pool to swim what you 'want' to swim in your race. In this case, we are talking about an Ironman swim. 2.4 miles. 3,863 meters. 4,224 yards.
Do you know what swim pace a 1:10 swim is? 90 minutes for an Ironman swim? How fast is that? Is there a difference in your open water swimming and your pool swim...yes. How much difference is hard to quantify. For simplicity sake, let's say your open water swim pace is 10% slower than your pool pace. At the faster end of the swim it might be a bit closer. At the slower end, it might be a bit slower than 10%.
What do you need to swim in the pool to approximate your IM swim goal pace? You have to swim faster in the pool. Faster because we aren't taking a possible draft effect or wetsuit effect into it.
It's not fast. It's not really fast for the fast pros. It certainly is not not fast for a 25, 50, 100, or a 400. But, you have to swim a LOT of them. Yes, it's technique because issues in the pool are magnified in open water. Yes, it's talent. But, it's not 'that' fast. It's about knowing your paces and effort, how they feel in the pool, and when possible figuring out how they compare in open water if you have a big difference.
And, it's about swimming enough of a distance at your pace to know that you can do it on race day.